Magnetic core structure



March 9, 1965 F. w. BENKE 3,173,113

MAGNETICCORE STRUCTURE Filed Dec. 7, 1960 WITNESS s I INVENTOR (33 3 Frank W. Benke w W4 wiECOMZCAIJL ATTORNEY United States Patent 3,173,113 MAGNETIC CORE STRUCTURE Frank W. Benito, Hickory Township, Mercer County, Pa, assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa, a corporation of Pennsylvania Filed Dec. 7, 1960, Ser. No. 74,376 7 Claims. (Cl. 336-60) -This invention relates to electrical inductive apparatus, such as transformers, and more particularly to magnetic core structures for such apparatus.

In electrical inductive apparatus, such as transformers and reactors, certain types of magnetic core structures are employed which include at least portions having a cross-sectional area of the cruciform or stepped type. The latter portions of a magnetic core structure may be conveniently formed from a plurality of assembled laminations of different widths with the widest laminations normally being disposed in the central portion of the cross-sectional area. As the required ratings of electrical inductive apparatus, such as transformers, increase, the physical size of magnetic core structures employed in such apparatus also increase. Where larger magnetic core structures include portions having a cross sectional area of the cruciform type, a cooling problem may result due to the distance that the heat must travel from the interior of the widest laminations which are normally included in the central portion of the cross section area to the edges or sides of such laminations. The latter heating results because of the losses in the magneticcore structure during the operation of the associated apparatus and such heat is normally dissipated or carried off by an associated cooling medium, such as insulating oil or other fluid, which passes over the outer edges of the laminations in the magnetic core structure.

One solution to the above cooling problem which has been employed in the past is to provide one or more spacing members which are disposed between the widest laminations in a magnetic core structure of the type described to permit the flow of a cooling medium in the ducts or passageways thus formed and reduce the distance of the heat transfer paths from the interior of the widest laminations to the cooling medium which carries off the heat from the magnetic core structure. In addition to the necessity for providing special spacing members, the latter construction has the additional disadvantage that the effective cross-sectional area of the magnetic core structure is reduced by the presence of the spacing members thus adversely affecting the space factor of the core and coil assembly in which the magnetic core is employed and increasing the size and weight of the overall core and coil assembly. It is therefore desirable to provide an improved magnetic core structure of the type described which overcomes the cooling problem in the central portion of the magnetic core structure while providing an increased or greater crosssectional area of the magnetic material compared to conventional magnetic core structures of the same general type.

It is an object of this invention to provide a new and improved magnetic core structure for electrical inductive apparatus.

Another object of this invention is to provide a new and improved means for cooling magnetic core structures.

A more specific object of this invention is to provide a new and improved means for cooling portions of a magnetic core structure having a cross-sectional area of the cruciform or stepped type.

Other objects of the invention will, in part, be obvious H and will, in part, appear hereinafter.

For a fuller understanding of the nature and objects, reference should be had to the following description taken in connection with the accompanying drawing in which:

FIGURE 1 is a front elevational view of a transformer core and coil assembly embodying the teachings of the invention;

FIG. 2 is a front elevational view of several layers of laminations which may be employed in the magnetic core structure of the core and coil assembly shown in FIG. 1; and

FIG. 3 is a partial view in section of the magnetic core structure shown in FIG. 1 taken along the line IIIIH.

Referring now to the drawings and FIG. 1 in particular, there is illustrated a transformer core and coil assembly 10 embodying the teachings of the invention. In this example, the core and coil assembly 10 comprises a three-phase magnetic core structure 30 of the core form type which includes the first and second outer leg portions 32 and 36, respectively, the central leg portion 34, and the upper and lower yoke portions 33 and 35, respectively, connecting the ends of said leg portions to form a substantially rectangular core structure having two substantially rectangular windows, and the three electrical phase windings 20A, 20B and 20C which are inductively disposed on the leg portions 32, 34 and 36, respectively, of the magnetic core structure 39.

More specifically, the magnetic core structure 30 comprises a plurality of assembled or stacked layers of laminations formed from magnetic sheet or strip material having at least one preferred direction of orientation or easier magnetization substantially parallel to the longitudinal dimension of said sheet or strip material or substantially parallel to the edges of said sheet or strip material, such as cold rolled silicon steel. For example, referring to FIG. 2, there are illustrated first and second layers of laminations which are suitable for use in the magnetic core structure 30 as illustrated. As disclosed in greater detail in US. Patent 2,300,964, issued to Putman, each of the layers of laminations shown in FIG. 2 includes the first and second outer leg laminations 52 and 54, respectively, the central leg lamination 56, the first and second upper yoke laminations 62 and 64, respectively, and the first and second lower yoke laminations 72 and 74, respectively. At least the major portion of both ends of the outer leg laminations S2 and 54 and the yoke laminations 62 and 74 is cut diagonally with respect to the longitudinal dimension of the strip material from which said laminations are formed. Both ends of the central leg lamination 56 are cut to be generally V-shaped while one end of each of the yoke laminations 64 and 72 is similarly cut to be generally V-shaped. The other end of each of the yoke laminations 64 and 72 is cut diagonally with respect to the longitudinal dimensions of the strip material from which said laminations are formed. As shown in FIG. 2, the adjacent ends of the yoke and leg laminations in each layer meet in substantially mitered butt joints which are of the diagonal type in order that magnetic flux may travel between the diiferent portions of the magnetic core structure 30 in substantially a continuous straight line to reduce the effective reluctance of the magnetic core structure 39. As mentioned previously, the laminations in each layer are assembled around two substantially rectangular windows to form a magnetic core structure which is substantially rectangular in configuration. The laminations in adjacent layers of the magnetic core structure are preferably reversed during stacking or assembly in order that the joints between the corresponding laminations in adjacent layers will be overand 200 shown in FIG. 1.

lapped by the laminations in the adjacent layer to form combination butt-lap joints as indicated at 82 and 84, respectively, in FIG. 2 for the lower left hand corner of the two layers of laminations shown. It is to benoted that for the lamination shapes shown in FIG. 2, the

width of the yoke laminations 62, 64, 72 and 74 must be greater than the width of the associated leg lamina- "tions 52, 54 and 56 in order to provide an area of overlap between the adjacent joints of the corresponding laminations in successive layers.

Referring now to FIG. 3, there is illustrated the crosssectional area of the Winding leg portion 32 of the magnetic core structure 30, which is of the cruciform or stepped type, in order that the magnetic core structure 30 be adapted for convenient assembly with associated electrical windings of the preformed type having an internal opening which is substantially circular in configuration, such as the electrical phase windings 20A, 208 In general, the winding leg portion 32 comprises a plurality of groups or portions 32A through 32E of laminations formed from magnetic strip or sheet material of different widths, each of said groups including a plurality of assembled or stacked laminations having a common shape, such as the leg lamination 52 shown in FIG. 2. The widths of the laminations included in the respective groups of the winding leg portion 32 decrease in steps in both directions away from the central or intermediate group or portion 32C.

More specifically, the central or intermediate group 32C of the winding leg portion 32 comprises a first plurality of laminations 96 each being of a first predetermined width and a second plurality of laminations 98 each being of a second predetermined width less than the first predetermined width of the laminations '96. The central group or portion 32C is formed predominantly of the wider laminations 96 while the narrower laminations 98 are periodically interspersed or interposed between the wider laminations 96 during the assembly or stacking of the winding leg portion 32 to provide a plurality of ducts or slots 42 at both sides or edges of the winding leg portion 32 to permit the passage of a cooling medium, such as an insulating oil therethrough in a substantially vertical direction through the winding leg portion 32. It is to be noted that the layers of the narrower laminations 98 include yoke laminations in order to form closed magnetic paths in the different portions of the magnetic core structure 30 and also to provide cooling ducts or slots in the upper and lower yoke portions 33 and 35, respectively, in which a cooling medium would flow in a substantially horizontal direction. The cooling ducts or recesses 42 which are thus formed are disposed substantially parallel to one another and spaced apart from one another as required in a particular application. The depths of each of the ducts 42 depends upon the difference in widths between the wider laminations 96 and the narrower laminations 98 and the width of each of the ducts 42 depends upon the number of narrower laminations 98 which are interposed between the adjacent wider laminations 96.

Each of the outermost groups of laminations 32A and 32E of the winding leg portion 32 comprises a plurality of laminations 92 having a predetermined Width which in this case is substantially the same as the width of the narrower laminations 98 of the central portion or group 320. Each of the intermediate groups of laminations 32B and 32D of the winding leg portion 32 also comprises a plurality of assembled laminations 94 having ,a predetermined width less than the width of the wider laminations 96 of the central group 32C but greater than the width of the laminations 92 of the outermost groups 32A and 32E. It is to be understood that for convenience during the manufacture of the magnetic core structure 30, the width of the narrower laminations 93 of the central portion 32C may be substantially 4 the same as the width of the laminations employed in one of the groups 32A-32E or 32B-32D having a width less than that of the wider laminations 96 of the central group 32C and that cooling ducts or recesses may also be provided in certain of the latter groups by the use of narrower laminations interposed in the same manner as in the group 32C.

In the operation of the core and coil assembly 10, heating results in the different portions of the magnetic core structure 30 due to the core losses therein. Such heat may be dissipated or carried off by an associated cooling medium in which the core and coil assembly 10 is immersed or which flows around the magnetic core structure 30 in thermal contact therewith. The presence of a plurality of relatively thin cooling ducts 42 in the widest portion of the cross-sectional area in the different closed loops provided in the magnetic core structure 30 results in an increased area of heat "transfer and tie creases the distance which the heat must travel from the interior of the wider laminations 96 of the central group 32C in the different portions of the magnetic core structure 30 in order to be carried off by the associated cooling medium. The latter increased area of heat transfer which extends longitudinally or axially of the adjacent laminations is also provided with an increase in the effective cross-sectional area of the magnetic material in the different portions of the magnetic core structure compared with conventional cooling duct arrangements in magnetic cores which have been employed in the past. In effect, the wider laminations in the central portion 32C of the magnetic core structure 30 function both as cooling members or fins and as magnetic core members in the arrangement disclosed. In other words, if the magnetic core structure 30 is employed with preformed electrical windings having a substantially circular internal opening, a greater percentage of the latter opening will be filled with magnetic material in a magnetic core structure as disclosed while still overcoming the heat transfer problems that would otherwise exist in conventional magnetic cores of the same general type.

It is to be understood that the teachings of the invention may be incorporated in magnetic core structures of the wound type in which the cross-sectional view of FIG. 3 would indicate the different widths of magnetic strip or sheet material that will be required during the winding of such a magnetic core. It is also to be understood that the teachings of the invention may be extended to either single phase or three-phase magnetic cores of either the core form type, as illustrated in FIGS. 1 and 2, or of the shell form type having a cross-sectional area which is either rectangular or generally semi-circular in configuration, such as would result if the cross-sectional area shown in FIG. 3 were divided in two along a vertical axis. The latter magnetic cores might either be of the assembled or stacked type, as illustrated in FIGS. 1 and 2, or of the wound type as just mentioned. I

It is also to be understood that the laminations of the magnetic core structure 30 may be formed from other suitable types of magnetic material, such as sheets of silicon-iron and aluminum-iron alloys containing from 1 to 7% silicon and from 1 to 10% aluminum, respectively, the sheets of said alloys having grains whose crystal lattice structure comprises four cube edges perpendicular to the plane of the sheet, known as cube texture, either doubly oriented or randomly oriented. The major volumetric proportion of the sheets is composed of grains having a crystalline lattice structure such that a cube face lies substantially arallel to the surface of the sheet and in the double oriented material, four cube edges of the cube lattice are parallel to the rolling direction or edge of the sheet and four cube edges are transverse thereto. In the randomly oriented cube texture material, the grains may have eight cube edges randomly distributed parallel to the surface of the sheet.

One such doubly oriented cube textured silicon-iron alloy is that disclosed in copending application Serial No. 681,333, now abandoned, filed August 30, 1957, and in copending application Serial No. 19,440, now Patent No.

'2,992,951, filed April 21, 1960, which are both assigned to the same assignee as the present application.

The apparatus embodying the teachings of this invention has several advantages. For example, a magnetic core structure including at least one closed loop or magnetic path having a cross-sectional area in the cruciform or stepped type as disclosed includes a greater -cross-sectional area of the magnetic material while improving the cooling of the magnetic core structure due to thelosses therein. In addition, the lamination shapes required in the magnetic core may be utilized to form the cooling ducts as disclosed to thereby eliminate the need'for any special spacing or duct forming members. The number and size ofthe'coolingducts may be adjusted to the requirements of 'a particular application. The principle of the magnetic core structure disclosed may be applied to any magnetic core structure in which the cross-sectional area includes a first group of wider laminations and at least one group of narrower laminations, such as a magnetic core having a rectangular cross-sectional area with intermixed laminations of different widths.

Since numerous changes may be made in the above described apparatus, and different embodiments of the invention may be made without departing from the spirit and scope thereof, it is intended that all the matter contained in the foregoing description or shown in the accompanying drawing shall be interpreted as illustrative and not in the limiting sense.

. Iclaim is my invention:

l. A magnetic core comprising a plurality of layers of laminations of magnetic strip material assembled to form at least one closed loop having a cross-sectional area of the cruciform type, said core having a central portion, said central portion of said core including a first group of laminations predominantly formed from magnetic strip material of a first predetermined width, the balance of the laminations in said first group being of a second predetermined width less than said first predetermined width and interleaved with the laminations of said first predetermined width in said first group to provide a plurality of ducts through which a cooling medium may pass, the number of laminations of said first predetermined width being greater than the number of laminations of said second predetermined width in said central portion to make the ducts narrower than the distance between the ducts, a plurality of groups of other laminations disposed on opposite sides of said central portion, the widths of the laminations in the groups of said other laminations decreasing in steps in each group in a direction away from said central portion, and the width of the laminations in one of the groups of said other laminations being substantially the same as the width of the laminations of said second predetermined width in the first group.

2. A magnetic core comprising a plurality of layers of laminations of magnetic strip material assembled to form at least one closed loop having a cross-sectional area of the cruciform type, said core having a central portion, said central portion of said core including a first group of laminations predominantly formed from magnetic strip material of a first predetermined width, the balance of the laminations in said first group being of a second predetermined width less than said first predetermined width and interleaved with the laminations of said first predetermined width in said first group to provide a plurality of ducts through which a cooling medium may pass, said ducts being spaced apart from one another and extending longitudinally of the adjacent laminations, the number of laminations of said first predetermined width being greater than the number of laminations of said second predetermined width in said first group to make the ducts narrower than the distance between ducts, a plurality of groups of other laminations disposed on opposite sides of said central portion, the widths of the laminations in the groups of said other laminations decreasing in steps in each group in a direction away from said central portion, and the width of the laminations in one of the groups of said other laminations being substantially the same as the width of the laminations of said second predetermined width in the first group.

3. A magnetic core comprising a plurality of layers of laminations assembled around a substantially rectangular window to form at least one closed magnetic loop of leg and yoke portions, said laminations being formed from magnetic strip material, said layers of laminations being divided into a central group and other groups, said central group of layers of at least each leg portion including a first plurality of laminations of at least a first predetermined width and a second plurality of laminations of a second predetermined width less than said first predetermined width, said first plurality of laminations being interposed between said second plurality of laminations to provide a plurality of recesses. at the outer edges only of said central group of layers through which a cooling medium may pass, the number of wide laminations exceeding the number of narrow laminations in said central group to make the recesses narrower than the distance between recesses, the other groups of layers on opposite sides of said central group being formed from laminations of gradually decreasing widths in directions away from said central group of layers.

4. A magnetic core comprising a plurality of layers of laminations assembled around a substantially rectangular window to form at least one closed magnetic loop of leg and yoke portions, said laminations being formed from magnetic strip material, said layers of laminations being divided into a central group and other groups, said central group of layers of the leg and yoke portions including a first plurality of laminations of at least a first predetermined width and a second plurality of laminations of a second predetermined width less than said first predetermined width, said first plurality of laminations being interposed between said second plurality of laminations to provide a plurality of recesses at the outer edges only of said central group of layers through which a cooling medium may pass, the number of laminations of said first predetermined width exceeding the number of laminations of said second predetermined width in the central group to make the recesses narrower than the distance between recesses, said recesses extending axially of the laminations in said central group, and other groups of layers on opposite sides of said central group, said other groups of layers being formed from laminations of gradually decreasing widths in directions away from said central group of layers.

5. A magnetic core comprising a plurality of layers of laminations formed from magnetic strip material and assembled to form at least one closed loop having a crosssectional area of the cruciform type, said core having a central portion, said central portion of the core being formed mostly of laminations of a first predetermined width, the balance of the laminations in said central portion being of a second predetermined width less than said first predetermined width and interspersed with the laminations of said first predetermined Width in said central portion to form a plurality of cooling passageways at the outer edges of said central portion, the number of laminations of said first predetermined width being greater than the number of laminations of said second predetermined width in the central portion to make the distance between passageways greater than the width of the passageways, and at least first and second other portions of the core disposed on each side of said central portion, each said other portion including a plurality of laminations of widths less than the first predetermined width of the laminations in said central portion.

6. A magnetic core comprising a plurality of layers of laminations formed from magnetic strip material and assembled to form at least one closed loop having a crosssectional area of the cruciform type, said core having a central portion, said central portion of the core being formed mostly of laminations of a first ,predetermined width, the balance of the laminations in said central portion being of a second predetermined width less than said first predetermined width and interspersed with the laminations of said first predetermined width insaid central portion to form a plurality of cooling pasageways at the outer edges of said central portions, said cooling passageways being spaced apart'from one another and extending longitudinally of the laminations in said central portion to permit the passage of a cooling fluid therethrough, the number of laminations of said first predetermined width being greater than the number of laminations .of said second predetermined width in thecentral portion to make the distance between passagewaysrgreater than the width of the passageways, and at least first and second other portions of the core disposed on each side of said central portion and each said other portion including a plurality of laminations'of widths less than the first predetermined width of the laminations in said central'portion,'the second predetermined width of the laminations in said central portion being substantially the same as the width of the laminations in one of the other portions of the loop.

7. A magnetic core comprising a plurality of layers of laminations formed from magnetic strip material and assembled to form at least one closed loop having a crosssectional area of the cruciform type, said core having ,a central portion, said central portion of the core being formed mostly of laminations of a first predetermined width, the balance of the laminations in said central portion being of a second predetermined widthless than said first predetermined width and interspersed with the laminations of said first predetermined width in said central portion to form a plurality of cooling passageways at the outer edges of said centralportion, at least a portion of each passageway extending longitudinally of the adjacent lamination in 'a substantially vertical direction, the number of laminations of said first predetermined width being greater than the number of 'laminations of said second predetermined width in the central portion to make the distance between passageways greater than the width of the passageways, at least first and second other portions of the core disposed on each side of said central portion and each including a plurality of laminations of widths less than the first predetermined width of the laminations in said central portion, and the width of the laminations in one of the latter portions of the loop being substantially the same as the width of the laminations of said second predetermined width in the central portion.

References Cited by the Examiner UNITED STATES PATENTS 1,769,871 7/30 Unger 336-60 2,780,787 2/57 :Somerville 336-6l XR 2,910,663 10/59 Wilk et al 336-60 3,077,570 2/63 Popa 336-61 FOREIGN PATENTS 166,613 7/ 2 1 Great Britain. 231 ,025 3/25 Great Britain.

JOHN F. BURNS, Primary Examiner.

MILTON O. HIRSHFIELD, JOHN P. WI-LDMAN,

Examiners. 

1. A MAGNETIC CORE COMPRISING A PLURALITY OF LAYERS OF LAMINATIONS OF MAGNETIC STRIP MATERIAL ASSEMBLED TO FORM AT LEAST ONE CLOSED LOOP HAVING A CROSS-SECTIONAL AREA OF THE CRUCIFORM TYPE, SAID CORE HAVING A CENTRAL PORTION, SAID CENTRAL PORTION OF SAID CORE INCLUDING A FIRST GROUP OF LAMINATIONS PREDOMINANTLY FORMED FROM MAGNETIC STRIP MATERIAL OF A FIRST PREDETERMINED WIDTH, THE BALANCE OF THE LAMINATIONS IN SAID FIRST GROUP BEING OF A SECOND PREDETERMINED WIDTH LESS THAN SAID FIRST PREDETEMINED WIDTH AND INTERLEAVED WITH THE LAMINATIONS OF SAID FIRST PREDETERMINED WIDTH IN SAID FIRST GROUP TO PROVIDE A PLURALITY OF DUCTS THROUGH WHICH A COOLING MEDIUM MAY PASS, THE NUMBER OF LAMINATIONS OF SAID FIRST PREDETERMINED WIDTH BEING GREATER THAN THE NUMBER OF LAMINATIONS OF SAID SECOND PREDETERMINED WIDTH IN SAID CENTRAL PORTION TO MAKE THE DUCTS NARROWER THAN THE DISTANCE BETWEEN THE DUCTS, A PLURALITY OF GROUPS OF OTHER LAMINATIONS DISPOSED ON OPPOSITE SIDES OF SAID CENTRAL PORTION, THE WIDTHS OF THE LAMINATIONS IN THE GROUPS OF SAID OTHER LAMINATIONS DECREASING IN STEPS IN EACH GROUP IN A DIRECTION AWAY FROM SAID CENTRAL PORTION, AND THE WIDTH OF THE LAMINATIONS IN ONE OF THE GROUPS OF SAID OTHER LAMINATIONS BEING SUBSTANTIALLY THE SAME AS THE WIDTH OF THE LAMINATIONS OF SAID SECOND PREDETERMINED WIDTH IN THE FIRST GROUP. 